<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>assign</title>
</head>
<body>

</body>
</html>
<script>
    let a={a:10,b:{b:20}}
    let b=Object.assign({},a)
    console.log(b.a);
    a.b.b=30;
    console.log(b.b.b);

</script>